8. Zero Carbon House, Balsall Heath, Birmingham

This award-winning eco-extension has completely transformed the inner-city home of architect John Christophers. In building the first retrofit house in the UK to achieve the highest level in the government's code for sustainable homes, Christophers set out to prove that "green doesn't have to be dull. You don't have to have either green or architecture. You can have both. You must have both if you're to inspire people."

From the street, the house is unmissable. Rising from a row of traditional two-storey red-brick terraces built in the 1840s, it reaches upwards for maximum solar gain. The roof is pitched at a 30-degree angle and laden with 35 sq metres of solar panels. Angular wood-lined dormer windows jut out from the front facade, while an inverted L-shape fashioned from reclaimed brick frames the edge of the modern extension.

Zero Carbon House has an airtight membrane to keep draughts out and warmth in. The floors are made from rammed and polished red clay, dug from the foundations of the property. Photograph: Martine Hamilton Knight

An airtight membrane is buried in the walls and floor to keep draughts out and warmth in. The mature garden at the rear of the house provides shade in the summer and allows sunlight through in winter. The washing machine and toilets use rainwater gathered in a tank lurking in the cellar, while skylights minimise the need for electrical lights. Where lights are needed, Christophers has increased the colour temperature of the bulbs, creating the perception of warmth.

Chris Cousins, homes and communities manager for Breeam, the world-leading design and assessment centre for sustainable homes, has said that the building is "particularly notable for its use of materials which have low embodied energy characteristics, including recycled newspaper insulation. In all, 14 reclaimed materials are used in the project, including 200-year old Canadian honeydew maple boarding for stairs and window seats."

The bathroom. Photograph: Martine Hamilton Knight

The floors are made from rammed and polished red clay, dug from the foundations of the property. The kitchen counters are made from recycled glass, while the dining tabletop is a repurposed building site sign. The stair rail is made of hemp, deliberately chosen by Christophers for its eco-credentials.

The Christophers household doubled their living space for around £350,000 and threw a big party to celebrate the day they were disconnected from the mains. "We see [the house] as a contribution to the groundswell towards green lifestyles and the enjoyment of a sustainable way of life," says Christophers. "It is designed to protect the environment and enable its occupants to enjoy the environment."